Users unable to login to Citrix Web Interface. When observing the Event Viewer, Event ID 30024 and 31003 appear with the following errors:
The XML document sent by the Citrix servers could not be processed because it contains invalid XML. This message was reported from the XML Service at address . The specified Citrix XML Service could not be contacted and has been temporarily removed from the list of active services.
All the Citrix XML Services configured for farm xxxxxxx failed to respond to this XML Service transaction.Background
This issue can be caused by several different issues, including DNS issues, firewall issues on the XenApp servers, XML service not running on the XenApp servers and even a few known issues with corrupt XML files. None of these were the cause of this particular issue. What led me to this conclusion is a tool called Citrix Medevac. Medevac was able to connect to the XML data on the XenApp 6.5 farm, which immediately told me XenApp itself was good to go, even DNS issues were ruled out.
In the end this was caused by our endpoint protection software G-DATA. It wasn't even in the firewall area as first expected. They have a web protection component that works perfectly on the XenApp servers but caused issues with TCP/80 traffic initiated by the server. Disabling Web > Process Internet Content resolved the issue.